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In computational chemistry, post–Hartree–Fock [1] [2] (post-HF) methods are the set of methods developed to improve on the Hartree–Fock (HF), or self-consistent field (SCF) method. They add electron correlation which is a more accurate way of including the repulsions between electrons than in the Hartree–Fock method where repulsions are ...
The first term in the above expansion is normally the Hartree–Fock determinant. The other CSFs can be characterised by the number of spin orbitals that are swapped with virtual orbitals from the Hartree–Fock determinant. If only one spin orbital differs, we describe this as a single excitation determinant.
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Møller–Plesset perturbation theory (MP) is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry.It improves on the Hartree–Fock method by adding electron correlation effects by means of Rayleigh–Schrödinger perturbation theory (RS-PT), usually to second (MP2), third (MP3) or fourth (MP4) order.
The origin of the Hartree–Fock method dates back to the end of the 1920s, soon after the discovery of the Schrödinger equation in 1926. Douglas Hartree's methods were guided by some earlier, semi-empirical methods of the early 1920s (by E. Fues, R. B. Lindsay, and himself) set in the old quantum theory of Bohr.
The foundations of the ROHF method were first formulated by Clemens C. J. Roothaan in a celebrated paper [1] and then extended by various authors, see e.g. [2] [3] [4] for in-depth discussions. As with restricted Hartree–Fock theory for closed shell molecules, it leads to Roothaan equations written in the form of a generalized eigenvalue problem
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For example, the electronic configuration of the H 2 O molecule is (1a 1) 2 (2a 1) 2 (1b 2) 2 (3a 1) 2 (1b 1) 2, [10] where the symbols a 1, b 2 and b 1 are orbital labels based on molecular symmetry. From Koopmans’ theorem the energy of the 1b 1 HOMO corresponds to the ionization energy to form the H 2 O + ion in its ground state (1a 1) 2 ...